1. Field of the Invention
This invention relates to disposable filter units.
2. Prior Art Relating to the Disclosure
Automatically operated analytic instruments for processing substances such as blood serum require that the blood serum be filtered to avoid clogging of the instrument with coagulated material and other solids. Therefore, individual quantities of blood to be analyzed are poured into disposable filter units and the filtrate is collected in sample cups for further processing. U.S. Pat. No. 3,608,736 describes a disposable filter unit having a downwardly depending cap which fits around the top portion of a sample cup, making it hard to determine the level of filtered blood serum in the cup. Since the interior surface of the cap frictionally engages and seals against the outside surface of the sample cup, small holes are provided directly through the wall of the cap for letting air escape from the cup as it is filled. A disadvantage of that type of cap is that it will only fit a specimen cup having a certain outside diameter. The outside diameters of sample cups produced by different manufacturers vary considerably, even if their inside diameters are the same. The end result is that different sizes of filtration units are required to be manufactured and stocked for each sample cup type. Obviously, this is inefficient and expensive. Prior disposable filtration units have a relatively small discharge hole at the bottom of the column so that the filter material, such as thin sheets of filter paper, is adequately supported by the column.
Many other biological substances are first filtered prior to being analyzed or processed in containers such as test tubes or the like. The filtering equipment is sometimes complicated and expensive. For example, a hollow cylindrical collection tube has a filter located at its lower end and a seal positioned around the outside of its lower end. The seal slides along the inside surface of a larger cylindrical test tube containing the fluid substance to be filtered. As the collection tube is pushed down into the larger test tube, pressure on the confined fluid forces fluid up through the filter and up into the collection tube. The filtered fluid is then transferred from the collection tube to a test tube or the like for analysis or further processing. Obviously, this apparatus is expensive to manufacture, requires an operator's time, and involves transferring fluids to an intermediate container, that is, the collection tube, increasing the possibility of contamination. Pressurization of the fluid being filtered may force undesired substances through the filter media.